ChannelSPURIOUS EMISSIONS
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Episode 7 · WSPR and FT8 · Series 01: The Listening Station

How far does a whisper travel?

A frame from the draft of episode 7, WSPR and FT8Coming soon
Release
Length
3:02
On the dial
14 MHz and more
Signal
FT8 and WSPR

What it covers

WSPR and FT8 are tiny, slow radio signals that amateurs all over the world send with a few watts or less. A computer can decode them far below the noise, because each message says almost nothing and says it very slowly. I explain what one WSPR message and one FT8 message hold, why every station starts on an exact clock, and how my station listens on every shortwave band at once and counts where the signals came from.

The written guide: set this up yourself

Chapters

  1. 0:00Intro
  2. 0:23Slow on purpose
  3. 0:49Two messages
  4. 1:24The clock
  5. 1:47Every band at once
  6. 2:18Where from
  7. 2:38What it is for

Frames from the draft

WSPR and FT8: Intro
01 Intro
WSPR and FT8: Slow on purpose
02 Slow on purpose
WSPR and FT8: Two messages
03 Two messages
WSPR and FT8: The clock
04 The clock
WSPR and FT8: Every band at once
05 Every band at once
WSPR and FT8: Where from
06 Where from
WSPR and FT8: What it is for
07 What it is for

Gear in this episode

RX-888 Mk IIthe receiver that hears all of shortwave at once (mine is from OpenSourceSDRLab)
MLA-30+ loop antennathe small active loop antenna for shortwave
TAPR RF Limiterprotects the receiver input from strong signals
HP EliteDesk small form factor PCthe shortwave computer I call Raphael (mine was rescued from e-waste)
CyberPower CP1500PFCLCD UPS (1500 VA, sine wave)the battery backup that keeps almost all of my station running through a power cut

Software and references

WSJT-Xwsjt.sourceforge.iothe program that WSPR, FT8 and FT4 come from. It includes wsprd, the WSPR decoder I run
ft8_lib (ka9q fork)github.comthe source of decode_ft8, the FT8 and FT4 decoder I run
ka9q-radiogithub.comthe program that cuts one channel for each band out of the receiver's stream (episode 5)
The FT4 and FT8 Communication Protocolswsjt.sourceforge.iothe paper by the authors of the modes: bits, tones, timing and sensitivity

What is simplified, and what is invented

  • No callsign and no locator appears in this video. Grey blocks stand in for station names and locations in the example messages. The power level in the WSPR example is invented.
  • The counts are one day from my station, rounded. Only totals are kept: by mode, band, hour, world region and distance band.
  • World regions are counted with rough latitude and longitude boxes. Distance is measured from downtown Seattle, a public landmark.
  • Map squares are 10 degrees wide and show three shades, not counts. The mark for my region shows the region only.
  • The noise picture in scene 1 is an illustration with an invented signal. Real decoders do more than add up: they also use strong error correction.
  • The message drawings show standard messages and leave out the error-correction bits. Bits and seconds are to scale.
  • The waterfall in scene 3 is an illustration, not a recording. The width and the length of each signal are to scale.
  • In the band and hour chart, each row is scaled to its own busiest hour. The daylight bar is rough.
  • World coastline: Natural Earth (public domain).